2004 Ram 5.7 Hemi 200,000 miles. New water pump, radiator, hoses, no leaks, no white smoke, no loss of coolant. Heat gage stays at the 12 o'clock position but will rise to 1 o'clock position at idle when outside air temp reaches 90 degrees . But will drop to normal when driving down road. So - head gasket? Thermostat? Any help would be appreciated..

 

Fan clutch, or electric cooling fan. Either that, or its perfectly normal behavior for when it is that hot out.

 

Found issue - It was radiator cap! Some crack in sealing gasket. Bought a new one and issue went away.

 

Good to hear it was an inexpensive and easy fix.